Running a pair of bevel or hypoid gears together in mesh for testing purposes in order to determine their running qualities and/or tooth bearing contact is well known in the art of gearing. Machines for performing such testing are equally known and are generally exemplified by U.S. Pat. No. 3,795,143 to Deprez et al.
In testing bevel or hypoid gears to determine the pattern of contact between the teeth of the gear pair, it is customary to coat the tooth surfaces of one member of the pair, usually the gear member, with a marking compound and then run the pair together under a light load. Marking compound will be removed from areas of the gear tooth surface which come into contact with tooth surfaces of the mating pinion member resulting in a contact pattern or "footprint" being revealed on the tooth surfaces of the gear.
In evaluating the contact patterns on tooth surfaces, it has been the practice to visually inspect the pattern on each tooth to determine if a part is accepted or rejected. If contact patterns are deemed to be out of the desired position, adjustments are made to the relative positions of the gear pair which will yield the desired patterns of contact.
Aside from the visual approach being time consuming, the procedure is not always accurate in that the relative position of the eyes of the viewer is likely to change from gear-to-gear. Thus tooth contact patterns will be evaluated from a slightly different point of origin. Also, it is the nature of the human eye to evaluate a contact pattern as though the tooth surface were flat when in fact, tooth surfaces of bevel and hypoid gears are usually curved in both profile and lengthwise directions, further adding visual distortion to the viewed contact pattern.
Attempts have been made to replace human visual inspection of contact patterns with electronic capturing of a tooth contact pattern. One such approach is shown in U.S. Pat. No. 5,373,735 to Gutman wherein a strobe light and charge coupled device (CCD) video camera are timed with the rotation of a gear member to capture individual contact patterns of successive teeth while the gear member is rotating. The images are digitized and stored in a computer for analysis and may be displayed individually or several may be superimposed on one another to illustrate tooth-to-tooth changes in the contact pattern.
Another manner in which to gear tooth contact patterns may be evaluated is shown in Japanese published patent application no. 04-36632 to Mazda Motor Corporation. This disclosure teaches coating the tooth surfaces with a type of paint substance and viewing the painted tooth surfaces with a CCD camera and storing the images in a computer. The gear pair is run together and the tooth surfaces are again viewed with the video camera to obtain another set of images. The painted image of each tooth after running the gear pair together is then subtracted from the respective painted image obtained prior to running. What remains is illustrative of the contact pattern.
One significant problem inherent in both methods discussed above is that although a contact pattern for each tooth surface is produced, there is no point of reference available when the image is viewed. In other words, the contact image is not assigned to any particular coordinate system (two-dimensional or three-dimensional) which makes it impossible to know the exact location of the contact pattern on the tooth surface. Viewing the contact pattern is insufficient if there is no reference to its position with respect to a tooth surface in that although the shape of contact may be defined, its position relative to the boundaries of the tooth surface is not known and, therefore, a complete and thorough evaluation of the tooth contact pattern cannot be conducted.
Another disadvantage to the above processes, including human visual inspection, is that the contact pattern obtained is not in a form that will permit its direct comparison to ideal contact patterns obtained by tooth contact analysis (TCA) methods. TCA patterns are represented as axial plane projections of a contact pattern on an appropriate tooth surface. Positioning of the contact pattern on a surface representative of the appropriate tooth is not found in the teachings discussed above.
It is an object of the present invention to provide a method of determining contact patterns of gear tooth surfaces by video digital imaging and providing an accurate frame of reference in which to consider the results obtained.
It is a further object of the present invention to simultaneously view and consider image data from a plurality of tooth surfaces in contrast to single tooth viewing methods of the prior art in order to obtain a consolidated contact pattern representative of a plurality of successive tooth surface contact patterns.